a)[(x + 174 : 3) * 3 + 4 ] = 1991
[(x +58) * 3 + 4 ] = 1991
[3*(x +58)+ 4 ] = 1991
(3*x +174+ 4) = 1991
3x+178=1991
3x=1991-178
3x=1813
x=1813/3
b)[15*(10x - 11 ) -120 ] * 10 - 125 = 25
(150x - 165 ) -120 ] * 10 - 125 = 25
(150x - 285) * 10 - 125 = 25
(1500x - 2850 - 125) = 25
(1500x - 2975) = 25
1500x=2975+25
1500x=3000
x=3000/1500
x=2